Gyratory crushers are used for crushing ore, mineral and rock material to smaller sizes. Typically, the crusher comprises a crushing head (referred to as a mantle) mounted upon an elongate main shaft. A first crushing shell is mounted on the crushing head and a second crushing shell is mounted on a frame such that the first and second crushing shells define together a crushing chamber through which the material to be crushed is passed. A driving device positioned at a lower region of the main shaft is configured to rotate an eccentric assembly positioned about the shaft to cause the crushing head to perform a gyratory pendulum movement and crush the material introduced in the crushing chamber. Example gyratory crushers are described in WO 2004/110626; WO 2008/140375, WO 2010/123431, US 2009/0008489, GB 1570015, U.S. Pat. No. 6,536,693, JP 2004-136252, U.S. Pat. No. 1,791,584 and WO 2012/005651.
The main shaft is supported at its uppermost end by a top bearing housed within a central hub that forms a part of a spider assembly mounted on top of the topshell frame part. Spider arms project radially outward from the central hub to contact an outer rim at the top shell. The material to be crushed typically falls through the region between the spider arms and is prevented from causing damage to the arms by shields mounted over and about each arm. Example shields are disclosed in U.S. Pat. No. 2,489,936; U.S. Pat. No. 2,832,547; U.S. Pat. No. 3,026,051; US 2002/0088888; US 2011/0192927. It is noted, these shields are typically secured to the spider arm via attachment bolts that project axially downward relative to the longitudinal axis of the main shaft. However, such configurations are disadvantageous as the bolt heads are exposed to the crushable material as it falls into the crushing chamber. With use, the bolt heads become damaged leading to attachment failure and subsequent loss of the shield that falls downwardly into the crushing chamber.
An alternative method of shield attachment involves welding the guards to the uppermost region of the spider arms. However, the welding process is both labour and time intensive and introduces additional problems when the worn shield needs removing. Additionally, the welding creates tension and stress concentrations into the spider arms. What is required is a spider arm shield that addresses the above problems.